1. Field of the Invention
The present invention relates to a substrate damage detection device for detecting damage made to a substrate such as a liquid crystal substrate when the substrate is being transferred by a substrate transfer robot between a plurality of processing chambers in a substrate processing system. The invention also relates to a substrate transfer robot provided with such a substrate damage detection device and to a substrate damage detection method.
2. Description of the Related Art
In a substrate processing system, when a substrate transfer robot transfers a substrate between chambers such as processing chambers, damage to the substrate, such as breakage or cracking, may be made due to e.g. contact of the substrate with a chamber. To remove such a damaged or defective substrate from the substrate processing system, a substrate damage detection device has conventionally been proposed that is configured to detect damage to a substrate caused during when the robot transfers the substrate.
For instance, JP-A-2011-139074 discloses the technique of detecting damage to a substrate by using two optical sensors. The sensors are arranged at opposite sides of an entrance of a processing chamber. Through this entrance, a substrate is introduced into the processing chamber while being carried by a hand of a transfer robot. Each optical sensor includes a light-emitting portion for directing light and a light-receiving portion for receiving light reflected by the substrate when the substrate passes through the entrance. Damage to the substrate is detected based on the amount of light received by the light-receiving portion.
In the technique disclosed in this document, when the transfer robot transfers the substrate into or out of the processing chamber, the two optical sensors move relative to opposite edges of the substrate (the edges extending in parallel to the substrate introducing direction). When a large change is observed in the level of the signal outputted from the sensors, it is determined that damage has been made to the relevant portion of the substrate.
Patent Document 1: JP-A-2011-139074
According to the above-described substrate damage detection technique, detection of damage is possible only with respect to a pair of edges of a rectangular substrate. In other words, the above-described method cannot detect damage that has been made to another pair of edges, i.e., the front and rear edges of the substrate which extend perpendicularly to the substrate introducing direction. Moreover, in the case of a substrate having a shape other than a rectangle, i.e., a circular substrate, for example, the area for which damage detection is possible is more limited.
Further, according to the above-described substrate damage detection technique, a pair of optical sensors need to be arranged at the entrance of each processing chamber. Thus, a relatively large number of optical sensors are necessary.